1. Field of the Invention
This invention relates to improvements in methods and apparatus for automatically detecting the presence of holes in filled and sealed packed plastic bags of the type containing a product and a gas.
2. Prior Art
Filled and sealed plastic bags containing product and a gas, for example, potato chip or other snack food packages, must not contain holes in them. If such bags contain holes, product can leak from the bag and air in large quantities can get into the bag and affect the product. Therefore, such bags having holes in them are defective and even though filled with product, must be removed after packing and prevented from entering the stream of distribution.
At present, filled and sealed packed plastic bags of snack food products are individually and manually inspected for holes and other defects at the time they are packed into a case or carton containing multiple bags. Obviously if one of the bags in the case leaks, it causes problems for the whole case of product as it enters the chain of distribution.
While manual inspection during manual packing of bags in cases is usually quite satisfactory, it has the disadvantage of all manual operations in that it depends on humans, and humans err. Moreover, there is presently a trend toward automating the case packing operation so as to eliminate the previous manual operation of packing the case. The workers who previously packed the case were the same ones who simultaneously inspected the bag for holes. Consequently, if cases were packed by automation, the workers would not be present to detect holes in the bag and many more bags with holes in them would likely enter the stream of distribution.
Many of the holes in the bags are not in the face of the bags, but are in the seams or seals and may be due to defective seals which occur in making and filling the bag, rather than defective plastic film from which the bag is made or tearing of the film. Nevertheless, no matter what the cause of the hole in the bag, there is and has been for some time a need in the art for an automatic means and method for detecting holes in bags.
There is a machine which attempts to measure leakage in small sealed plastic bags containing product and a gas. In such construction the bag is precisely positioned on an inspection table and goes through five or six stations where at each station a weighted member is dropped on the bag to be tested in order to force air out of any leaks in the bag without bursting the bag. The weights may be in the form of a "bed of nails." This device, however, is not completely satisfactory for several reasons. If a bag has more air or air pressure than usual, even the multi-station testing does not force enough air out of the bag when the bag has a leak. An optical arrangement is used for measuring at the end of the stations. In addition to other problems mentioned above, the known prior art is complex, wasteful of space, and subject to inaccuracies. Moreover, it cannot measure the rate of leakage and therefore is dependent on each bag having the same amount of air in it, something that does not occur in usual production lines.
It is particularly difficult to detect a hole in a filled and sealed plastic bag containing gas and a product such as potato chips and the like, other than doing it manually, because of the nature of the bag. That is, the gas in the bag is not under high pressure. The gas is usually air and gas detection methods are not appropriate. Because of significant graphics on the bag and because possible holes are in the seams, optical detection methods are not appropriate. It appears that there was no solution to this longstanding problem prior to the present invention.